This invention is in the field of carbon nanomaterials including fullerenes and, in particular, relates to the continuous synthesis of such materials. The invention more specifically relates to filter devices and methods for collection of carbon nanomaterials which provide for in situ cleaning to facilitate continuous operation.
The term “carbon nanomaterials” is used generally herein to refer to any substantially carbon material containing six-membered rings that exhibits curving of the graphite planes, generally by including five-membered rings amongst the hexagons formed by the positions of the carbon atoms, and has at least one dimension on the order of nanometers. Examples of carbon nanomaterials include, but are not limited to, fullerenes, single-walled carbon nanotubes (SWNTs), multiple-walled carbon nanotubes (MWNTs), nanotubules, and nested carbon structures with dimensions on the order of nanometers. The term “fullerene” is used generally herein to refer to any closed cage carbon compound containing both six-and five-member carbon rings independent of size and is intended to include the abundant lower molecular weight C60 and C70 fullerenes, larger known fullerenes including C76, C78, C84 and higher molecular weight fullerenes C2N where N is 50 or more. The term is intended to include “solvent extractable fullerenes” as that term is understood in the art (generally including the lower molecular weight fullerenes that are soluble in toluene or xylene) and to include higher molecular weight fullerenes that cannot be extracted, including giant fullerenes which can be at least as large as C400. Carbon nanomaterials may be produced in soot and, in certain cases, carbon nanomaterials may be isolated from the soot or enriched in the soot. Soot produced during the synthesis of carbon nanomaterials, such as fullerenes, typically contains a mixture of carbon nanomaterials which is a source for further purification or enrichment of carbon nanomaterials or which may itself exhibit desired properties of carbon nanomaterials and be useful as an addition to convey those properties. The term “carbon nanomaterials,” when used without limitation, is intended to include soot containing detectable amounts of carbon nanomaterials. For example, the term “fullerenic soot” is used in the art to refer to soot containing fullerenes. Fullerenic soot is encompassed by the term carbon nanomaterials.
Various carbon nanomaterials have different potential uses based on their various properties. Fullerenes are potentially useful as therapeutics, in electronics processing and in energy conversion. Fullerenic soots may offer advantages in carbon blacks as sorbent or as additives in tire production. Nanotubes have potential application as reinforcements in composite materials, electronic devices and display technologies.
While the art recognizes significant potential for commercial application of carbon nanomaterials, the high costs and difficulty in obtaining these materials in large amounts necessary for developing these applications has been a major impediment in practical application of these materials.
Carbon nanomaterials, including fullerenes SWNTs and MWNTs, can be produced by a variety of methods including, without limitation, arc methods (e.g., U.S. Pat. Nos. 5,227,038 and 5,876,684); combustion methods (U.S. Pat. Nos. 5,273,729; 5,985,232; and 6,162,411; Howard et al. (1991) Nature 352:139-141; Howard et al. (1992) J. Phys. Chem. 96:6657; Howard et al. (1992) Carbon 30:1183 and McKinnon et al. (1992) Comb. Flame 88:102; Taylor et al. (1993) Nature 366:728-731); electric beam evaporation (e.g., U.S. Pat. No. 5,316,636); laser ablation (Zhang et al. (1999) J. Phys. Chem. B 103:9450.)
In such processes, carbon nanomaterials are collected after generation inside a processing chamber, for example, by scraping product from collection surfaces (W. Kratschmer et al, 1990, Nature, Vol. 347, pp. 354-357), or outside the processing chamber in a tubular condenser (Lorents et al., U.S. Pat. No. 5,304,366), in a glass wool filter system (P. Hebgen and J. B. Howard, (1999) Fifth Int'l Microgravity Combustion Workshop, K. R. Sachsteder and J. S. T'ien (eds.) NASA/CP 1999-208917, p. 137) or in a bag-like paper filter (Makato, K. et al., 1995, Japanese Abstract JP7138009A2). A two stage collection method using a product recovery tank to collect most of the product in combination with a bag filter to capture additional product is reported in Katshuhide, M et al., 1994, Japanese Abstract JP6056414A2. None of these product collection methods, however, allow cleaning of the collection surface while carbon nanomaterial production is ongoing, unless more than one collector is used sequentially. Lorents et al., U.S. Pat. No. 5,304,366 report the use of multiple collectors for carbon nanomaterials where one collector can be taken off line, while the other collector remains in operation.
There is a need in the art for larger-scale generation and lower-cost production of carbon nanomaterials to facilitate their practical application. The development of continuous processes for synthesis of carbon nanomaterials is one way to scale up synthesis and decrease cost. To enable lower cost production of carbon nanomaterials, devices and collection methods that can operate without halting the synthetic processes are needed. There also exists a need in the art for collection devices and methods that are generally compatible with the variety of synthetic methods for carbon nanomaterials that are known in the art. The devices and methods herein provide such versatility and facilitate continuous operation.